The document discusses gamma irradiation induced band gap modifications in nanocrystalline vanadium oxide thin films. It describes how vanadium oxide thin films were synthesized using a sol-gel method and characterized after gamma irradiation at doses of 100 KGy and 300 KGy. The main results were that crystallinity decreased with higher gamma dose while electrical resistivity and optical band gap increased. Thermoelectric power also increased over the temperature range due to energy filtering of carriers at grain boundaries induced by gamma irradiation.

1. BY
Bilal Ahmad Bhat
Lecturer
Jammu and Kashmir
School Education
Gamma irradation Induced Band Gap Modifications in
Nanocrystalline Vanadium Oxide Thin Films

2. Introduction.
Experimental Details.
Results and Discussions.
Conclusions.
Plan of presentation

3. 1. Introduction
Vanadium oxide refers to:
• Vanadium(II) oxide ……………………(vanadium monoxide), VO
• Vanadium(III) oxide …………… (vanadium sesquioxide or trioxide), V2O3
• Vanadium(IV) oxide ………………….(vanadium dioxide), VO2
• Vanadium(V) oxide …………………..(vanadium pentoxide), V2O5
In addition to these principal oxides of vanadium, various other distinct phases exist:
Phases with the general formula VnO2n+1 . Examples V3O7, V4O9 and V6O13.
Phases with the general formula VnO2n−1 . Examples of V4O7, V5O9, V6O11,
V7O13 and V8O15.
1. Vanadium….. 3d transition element with
atomic no.23

4. 2. V2O5 is the saturated (highest oxidation state) in the V-O system and
consequently the most stable one among these vanadium oxides with
optical band gap ~ 2.1 eV.
3. It has a lamellar, or sheet like structure.
4.V2O5 in the form of thin films has attracted much attention due to its
unique electronic, chemical and optical properties.
5.Thin films of V2O5 have been prepared by different techniques
including:
(a) vacuum evaporation.
(b) sputter deposition.
(c) thermal oxidation
(d) pulsed laser deposition
(e) chemical vapor deposition
(f) sol-gel processes
(g) spray pyrolysis .

5. Due to the advantages of high purity, homogeneity, stoichiometry,
simplicity of equipments involved and cost effectiveness for large
scale production, the sol gel process has become one of the best
approaches to deposit metal oxide thin films.
7. V2O5 acts as a promising material for thermoelectric devices.
An important parameter characterizing thermoelectrical perforformance of
materials is the zT parameter.
S ………….Thermoelectric power (Seebeck coefficient).
ρ …………. Electrical resistivity.
κe …………… Electronic component thermal conductivity.
κl ………………Lattice component of the thermal conductivity.
T……………………. Absolute temperature .

6. Thus for a better thermoelectric performance.
S …………… high
ρ and κ .........low
Regrettably s, (ρ) and K vary in a noncomplementary way, preventing zT from
an excellent improvement, and these parameters are interrelated through the
carrier concentration (n)

7. synthesis
Modification Gamma Irradation
Sol-Gel With spin
coater on Glass
substrates
Characterization
2. Experimental Details

8. Step-2
Vanadium pentaoxide powder
Red brown Viscous sol
Spin
coat on
quartz
substrat
es
Overview of Sol gel synthesis of V2O5 thin films
Step -1
Step-3
sintering Pure V205
Thin films.
Pure V205
Thin films.
Gamma
irradation
Gamma irradiated
V205 Thin films.
Clear yellow solution
Red brown Viscous gel.

9. 3.Results and Discussions
1. Structural studies.
All the samples posses polycrystalline orthorhombic V2O5 phase [JCPDS file no. 85-0601]. The
relative high intensity of the (001) peaks demonstrates the growth of films oriented along the c-axis
perpendicular to the surface of substrate.
Intensity of diffraction peaks demonstrate that crystallinity Decreases with increasing gamma dose.
Sample D( nm) d (Å)
Pristine 27.4 4.31
100 KGy 22.6 4.34
300 KGy 14.5 4.36

10. 2. Electrical Studies
*All the samples show semiconducting
behavior as electrical resistivity
decrease with increasing temperature.
*Electrical resistivity increases with
gamma irradiation.
I . Resistivity Vs Temperature II . Seebeck coefficient Vs Temperature
*Negative value of S also demonstrate
that all films are n type
semiconductors.
*The S value increases significantly
over the entire temperature range
upon gamma irradation.

11. Variation of seebeck coefficient can be understood on the basis of phenomenon
of
Energy Dependent filtering of charge carriers along the grain boundaries and defects.
The value of thermoelectric power depends on the mean carrier energy relative to
the Fermi level . Therefore, this phenomenon of carrier energy filtering leads to
increase S value with decrease of grain size upon gamma irradiation.
Fig. Schematic representation of thermal diffusion of the electrons toward the colder side. Mechanism of
energy filtering of charge carriers by the potential barrier formed at the grain boundaries.

12. 3. Optical Studies
UV- Visible absorption spectra Tauc plot : Band gap variation
1. Shifting of absorption peak towards lower wavelength upon gamma irradation
indicates Blue shift upon gamma irradation
2. The optical band calculated from Tauc plot were found to get enhanced upon
gamma irradation which is due to quantum size effect.

13. 4. Conclusions
1. Gamma irradiation results decrease the crystallite size of V2O5 thin
films.
2. Resistivity of V2O5 thin films increase with increase in ion
implantation.
3. Thermo power of V2O5 thin films gets augmented upon gamma
irradation.
4. Optical Band gap of V2O5 thin Films gets augmented upon gamma
irradation.